Split blocks of video transcript into paragraphs

split.php

<?php

/* quick and dirty paragraph splitter
 * by Erorus
 * 
 * this script is fully in the public domain, do what you want with it
 *
 * intended for use for unformatted video transcripts
 * such as ones produced by Ars Technica, e.g.
 * https://cdn.arstechnica.net/wp-content/uploads/2018/04/3545034e-f60c-4657-b223-6cde51b5576fcc.txt
 */

define('PARA_LENGTH', 600);

$lines = file(__DIR__ . '/textblocks.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$paragraphs = [];
foreach ($lines as $line) {
    $paragraphs = array_merge($paragraphs, BuildPara($line));
}

echo implode("\n\n", $paragraphs), "\n";

function BuildPara($line) {
    $split = preg_split('/([\.\?!][^\w\s]*)(?: |$)/', $line, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

    $ret = [];
    $para = '';

    while (count($split)) {
        $words = array_shift($split);
        $punct = array_shift($split);

        $text = $words . $punct;

        if (substr($punct, 0, 1) == '?') {
            // sentence is a question, force into own paragraph
            if ($para) {
                // close prev paragraph
                $ret[] = $para;
                $para = '';
            }
            $ret[] = $text; // new paragraph is just the question

            continue;
        }
        if ($para) {
            $commaPos = strpos($text, ',');

            if (strlen($para) + strlen($text) > PARA_LENGTH // hit length limit on paragraph
                || ($commaPos !== false && $commaPos < 10)) { // sentence starts with introductory word, probable new thought/paragraph
                $ret[] = $para;
                $para  = '';
            }
        }

        $para .= ($para ? ' ' : '') . $text;
    }

    $ret[] = $para;

    return $ret;
}